servo_v4: Add servo_v4 device interfaces

Add i2c port selection, sx1505 interfaces to servod.
Add servo_v4 xml description. This covers partial support
for Servo V4, as it's USBPD implementation is incomplete.

BUG=chromium:571476
TEST=GPIO, I2C, console work with reworked servo_v4

Change-Id: I04201dd5c613f842660cd72b0b88c189711388a5
Signed-off-by: Nick Sanders <nsanders@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/329954
Reviewed-by: Todd Broch <tbroch@chromium.org>
8 files changed